In recent years, as part of a study of nanotechnology, an application study on particles having a particle diameter of several hundred nanometers or less has been actively conducted. In particular, hollow particles wherein silica or the like is used are also expected to have nano-sized one to deal with a trend of ultrafine technology that is typified by the nanotechnology. The hollow particles are hollow inside. Thus, for example, studies to utilize them as a sustained-release drug or a sustained-release cosmetic containing an active ingredient, as one for protecting a substance that is decomposed or deteriorated by contact with an outside environment, as a carrier for a drug delivery system or the like have been conducted. They are expected to be applied in various fields.
As an example of the hollow particles made by using the silica, there is an invention on highly dispersed hollow silica nanoparticles and a method for manufacturing the same described in a patent document 1. According to a description of the patent document 1, the hollow nanoparticles are hollow nanoparticles that comprise a dense silica shell and that have a primary particle diameter by a transmission electron microscopic method of 30 to 300 nm and a particle diameter by a static light scattering method of 30 to 800 nm, wherein pores of 2 nm to 20 nm are not detected in a pore distribution measured by a mercury intrusion method.